Different Concentrations Of NO2 Research Articles

Ag–CdS-Coated Cladding-Modified Fiber-Optic Sensor for Detection of NO2 Gas

In this study, a cladding-modified fiber-optic sensor is reported for NO2 gas detection. Monitoring the purity of air is the need of the hour, with the growing technologies. Hence, in this work, Ag-doped CdS is coated over the cladding-removed region of 3[Formula: see text]cm length by Chemical Bath Deposition (CBD) which acts as the gas-sensing medium. Ag–CdS is coated over four fibers each with a different coating duration of 10[Formula: see text]min, 20[Formula: see text]min, 30[Formula: see text]min and 40[Formula: see text]min. Characterization of Ag–CdS is done by Scanning Electron Microscope (SEM), UV-visible absorption spectroscopy and UV-visible reflectance spectroscopy. The spectral response for different concentrations of NO2 is studied on the four fibers separately, and it is analyzed and compared. The minimum detection limit is 100[Formula: see text]ppm and the response time is 10[Formula: see text]min. Out of the four fibers, Ag–CdS-30 exhibited the best response with a sensitivity of 15.5%. The results are compared with cladding-modified fiber coated with CdS, which was reported previously. The effect of Ag-doping is analyzed.

Enhanced response characteristics of NO2 gas sensor based on ultrathin SnS2 nanoplates: Experimental and DFT study

Layered-metal dichalcogenides with extraordinary characteristics of vast surface area, tunable bandgap and superior adsorption capability enable the potential for application in gas sensors. However, the synthesis of effective material for enhanced response performance remains a challenge. Herein, we exploited a fascinating sensitivity and selectivity towards NO2 gas detection using SnS2 nanoflakes prepared via the hydrothermal method. SnS2 nanoflakes with a thickness of 25 nm and an average diameter of approximately 500 nm show the potential for the detection of NO2 gas at low concentrations of ppb levels. The sensing properties of the SnS2 sensors were investigated for different concentrations of NO2 at various operating temperatures. The sensor exhibits the highest gas-sensing response of 161 at 250 οC upon exposure to 5 ppm of NO2 gas with fast response and recovery times. In addition, the sensor shows excellent selectivity with a low detection limit of ppb level. The electronic structure and gas-sensing mechanism are elucidated via finding density of states, charge density, and band structure based on DFT study which is calculated by the Vienna ab-initio simulation package (VASP). The considerable small adsorption energy reveals a physisorption of the NO2 molecules on the SnS2 surface (-0.174 eV), indicating the SnS2 nanoflakes are intriguing candidates for the speedy detection of NO2 gas.

Acidic Gas Determination Using Indium Tin Oxide-Based Gas Sensors.

This work has presented gas sensors based on indium tin oxide (ITO) for the detection of SO2 and NO2. The ITO gas-sensing material was deposited by radio frequency (RF) magnetron sputtering. The properties of gas sensing could be improved by increasing the ratio of SnO2. The response characteristics of the gas sensor for detecting different concentrations of NO2 and SO2 were investigated. In the detection of NO2, the sensitivity was significantly improved by increasing the SnO2 ratio in ITO by 5%, and the response and recovery time were reduced significantly. However, the sensitivity of the sensor decreased with increasing SO2 concentration. From X-ray photoelectron spectroscopy (XPS) analysis, the gas-sensitive response mechanisms were different in the atmosphere of NO2 and SO2. The NO2 was adsorbed by ITO via physisorption but the SO2 had a chemical reaction with the ITO surface. The gas selectivity, temperature dependence, and environmental humidity of ITO-based gas sensors were systematically analyzed. The high detection sensitivity for acidic gas of the prepared sensor presented great potential for acid rain monitoring.

Conversion of methylamine in a flow reactor and its interaction with NO

The conversion of methylamine (CH3NH2, 1000 ppm) has been studied in an atmospheric-pressure flow reactor from both experimental and modeling points of view. Several values of the oxygen excess ratio (λ), from pyrolysis to fuel-lean conditions, have been tested, and a large number of different species have been quantified experimentally by three different diagnostic techniques: gas chromatography, Fourier Transform Infra-red spectroscopy (FTIR) and an infra-red NO analyzer. For the first time, the influence of NO addition (500 and 1000 ppm) on the stoichiometric oxidation of methylamine has also been experimentally evaluated, and the main products of such interaction have been identified. Results indicate that, unlike the little influence of oxygen availability on methylamine conversion, the presence of different concentrations of NO promotes methylamine oxidation at lower temperatures. A literature mechanism has been validated against the present experimental data since previous experimental works under these conditions are scarce. The largest discrepancies have been found for the formation of NH3 and NO as oxidation products, which are under and overestimated by the model, respectively, and under pyrolysis conditions, where modification of the kinetic parameters for the reaction CH2NH2 ⇌ CH2NH + H from the original mechanism notably improves the agreement between experimental and simulated results.

Liquid Shear Exfoliation of MoS2: Preparation, Characterization, and NO2-Sensing Properties.

2D materials possess great potential to serve as gas-sensing materials due to their large, specific surface areas and strong surface activities. Among this family, transition metal chalcogenide materials exhibit different properties and are promising candidates for a wide range of applications, including sensors, photodetectors, energy conversion, and energy storage. Herein, a high-shear mixing method has been used to produce multilayered MoS2 nanosheet dispersions. MoS2 thin films were manufactured by vacuum-assisted filtration. The structural morphology of MoS2 was studied using ς-potential, UV-visible, scanning electron microscopy (SEM), atomic force microscopy (AFM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), X-ray diffraction (XRD), and Raman spectroscopy (RS). The spectroscopic and microscopic analyses confirm the formation of a high-crystalline MoS2 thin film with good inter-sheet connectivity and relative thickness uniformity. The thickness of the MoS2 layer is measured to be approximately 250 nm, with a nanosheet size of 120 nm ± 40 nm and a number of layers between 6 and 9 layers. Moreover, the electrical characteristics clearly showed that the MoS2 thin film exhibits good conductivity and a linear I-V curve response, indicating good ohmic contact between the MoS2 film and the electrodes. As an example of applicability, we fabricated chemiresistive sensor devices with a MoS2 film as a sensing layer. The performance of the MoS2-chemiresistive sensor for NO2 was assessed by being exposed to different concentrations of NO2 (1 ppm to 10 ppm). This sensor shows a sensibility to low concentrations of 1 ppm, with a response time of 114 s and a recovery time of 420 s. The effect of thin-film thickness and operating temperatures on sensor response was studied. The results show that thinner film exhibits a higher response to NO2; the response decreases as the working temperature increases.

Highly sensitive NO2 sensor based on mesoporous ZrO2–WO3 nanotubes composite

In this study, two anodic oxidation processes were used to prepare ordered mesoporous zirconia nanotubes. Ammonium metatungstate was introduced into zirconia to obtain mesoporous ZrO2–WO3 composite nanotubes. We performed XRD, TEM, and SEM tests on the material. Furthermore, a mixed electromotive force–based NO2 sensor was fabricated using ZrO2–WO3 nanotubes as sensing materials. The sensor not only has a low working temperature (400°C) and high sensitivity (131.4 mV/decade) but also shows remarkable selectivity, stability, and repeatability. At 400°C, the polarity curve of the sensor in air and under different concentrations of NO2 was measured, which proves the mixed electromotive force mechanism. Moreover, the tubular structure of the mesoporous ZrO2–WO3 composite provides additional electrochemical active sites, improves the catalytic efficiency, enhances the diffusion of NO2, and reduces NO2 consumption in the diffusion process, thus essentially improving the performance of the sensor.

Selective NO2 Detection of CaCu3Ti4O12 Ceramic Prepared by the Sol-Gel Technique and DRIFT Measurements to Elucidate the Gas Sensing Mechanism.

NO2 is one of the main greenhouse gases, which is mainly generated by the combustion of fossil fuels. In addition to its contribution to global warming, this gas is also directly dangerous to humans. The present work reports the structural and gas sensing properties of the CaCu3Ti4O12 compound prepared by the sol-gel technique. Rietveld refinement confirmed the formation of the pseudo-cubic CaCu3Ti4O12 compound, with less than 4 wt% of the secondary phases. The microstructural and elemental composition analysis were carried out using scanning electron microscopy and X-ray energy dispersive spectroscopy, respectively, while the elemental oxidation states of the samples were determined by X-ray photoelectron spectroscopy. The gas sensing response of the samples was performed for different concentrations of NO2, H2, CO, C2H2 and C2H4 at temperatures between 100 and 300 °C. The materials exhibited selectivity for NO2, showing a greater sensor signal at 250 °C, which was correlated with the highest concentration of nitrite and nitrate species on the CCTO surface using DRIFT spectroscopy.

Polymeric Nanofibriller Matrix on ITO Substrate for Flexible Chemical Sensing Applications

The authors present here a facile electrochemical approach to synthesize Poly(Aniline) nanofibriller matrix on ITO coated PET substrate for development of wearable or embeddable sensors. Electrochemical parameters were optimized for even diametric synthesis and controlled length of Poly (Aniline)) nanofibers. A three – step chrono potentiometric deposition was found to be efficient for the synthesis of the matrix. Precise tuning of galvanic conditions during the synthesis process was highly effective and repetitive towards controlling the nucleation of Poly (Aniline) seeds on the substrate that serves as the basis of nanofibers with presumable diameter range. Charge conduction behaviour of the matrix was studied via Linear Sweep Voltammetry and a semiconducting nature was observed. The synthesized nanofibrillar sensor platforms were subjected to Scanning Electron Microscopy (SEM), UV-VIS Spectroscopy and FTIR spectroscopy for elucidation of morphological and structural aspects. The distribution of nanofibers network throughout the substrate was uniform and dendritic. Flexibility characteristics of the sensors were studied by bending the sensor to different radii and in-situ monitoring of resistance. The synthesized sensor platforms were subjected to NO2 sensing in chemiresistive mode under dynamic conditions to investigate the applicability of the same under real-time applications. Upon exposure to different concentrations of NO2, the devices exhibit a rapid response at concentrations as low as 1 ppm. The betterment in overall sensing behaviour in comparison to conventional thin film type sensors could be attributed to the one-dimensional structure of nanofibers leading to effective diffusion on analyte molecules and low scattering loss during charge transport. These flexible sensors can be interesting for novel mobile applications.

Amperometric type NO2 sensor based on La0.75Sr0.25Cr0.5Fe0.5O3-δ-Bi2O3 sensing electrode prepared by self-demixing

Bi2O3 modified La0.75Sr0.25Cr0.5Fe0.5O3-δ (LSCF) composites have been successfully prepared by self-demixing and used as the sensing electrode (SE) of an amperometric NO2 sensor with yttria stabilized-zirconia (YSZ) electrolyte. The Bi2O3 modified LSCF composites were formed from precursor La0.75Sr0.25BixCr0.5Fe0.5O3+δ (x = 0, 5%, 10%, 20%, 30% and 40%) after calcining at 1200 °C. The particle size of LSCF was increased with the Bi2O3 content increasing. The YSZ porous framework structures were fabricated on YSZ to prolong TPB and the LSCF-xBi2O3-SE with porous structure was prepared on the porous YSZ backbone after calcining at 1000 °C. It is found that the sensors attached with LSCF-xBi2O3-SE are more sensitive to different concentrations of NO2 (25–300 ppm) than the LSCF-based sensor. Among them, LSCF-20% Bi2O3 based sensor exhibits the highest sensitivity (0.301 μA /ppm at 550 °C). The relationship between ΔIs and NO2 concentrations of the sensor varies linearly at a given temperature. Meanwhile, the sensor shows well anti-interference capability for co-existent gases.

Accurate quantification, naked eyes detection and bioimaging of nitrite using a colorimetric and near-infrared fluorescent probe in food samples and Escherichia coli

Nitrite (NO2−) is an inorganic contaminant that exists widely in the environment including water and food products, excessive amounts of NO2− would threaten humans and aquatic life. Developing a rapid and convenient sensing method for NO2− remains a great challenge. Herein, a colorimetric and near-infrared fluorescent probe (TBM) was synthesized and applied for sensitively and selectively detecting NO2− in water, food samples and Escherichia coli (E. coli). With the addition of NO2−, the probe TBM solution has a distinct visual color changed from red to colorless and fluorescence intensity at 620 nm quickly decreased. The probe TBM could detect NO2− quantitatively with a detection limit of 85 nM based on a 3σ/slope. Under optimum conditions, TBM has been successfully used to detect NO2− in real-world environmental and dietary samples, with positive results. Besides, paper strips loaded with TBM have been used to visually determine NO2− levels. Most importantly, TBM has also been proven to be able to discriminate from different concentrations of NO2− in E. coli by fluorescence imaging. In summary, the probe TBM was successfully developed for the accurate quantification, naked eyes detection and bioimaging of NO2− in water, food samples and E. coli, which provides a useful tool to better guarantee the quality and safety of daily life and food industry.

Experimental realization of visible gas sensing technology based on spatial heterodyne spectroscopy

Based on the characteristics of optical absorption gas sensing technology (OA-GST) and spatial heterodyne spectroscopy (SHS), a novel type of visual gas sensing technology (V-GST) can present the invisible gas information in the form of two-dimensional visual fingerprint, which has attracted people's attention. In this paper, we have realized the NO2 detection of V-GST in the laboratory environment for the first time. Experimental results show that: V-GST not only has different interferogram response to different spectra, but also has good response to different concentrations of NO2, which lays a foundation for the application of this technology in gas sensing. And the average classification recognition rate of the system for different band NO2 response data is over 80%, which verifies the effectiveness of the V-GST in gas detection.

Nickel-Decorated Black Phosphorus for Room Temperature NO2 Detection

Introduction In the rapidly emerging field of layered two-dimensional (2D) functional materials, bP, the all P-counterpart of graphene, is a potential candidate for various applications e.g., nanoscale optoelectronics, rechargeable ion batteries, electrocatalysts, thermoelectrics, solar cells, and sensors [1]. bP has been reported to exhibit superior chemical sensing performance. In particular, bP is selective for the detection of paramagnetic molecules, e.g., NO2, in addition to high sensitivity at a limit of detection (LOD) of ppb levels.[2] In this work, by applying a multiscale characterization approach we demonstrated a stability and functionality improvement of Nickel-decorated bP (Ni/bP) films for gas sensing prepared by a simple, reproducible and affordable deposition technique. Furthermore, we studied pos-sible electrical activity of these films for their employment as functional layers in gas sensors by exposing them to different gaseous compounds (NO2, CO2, H2, NH3, CO, Benzene, etha-nol, ethylene, Formaldehyde) in different relative humidity (RH%) conditions. Moreover, the influence in sensing perfor-mance of nickel nanoparticle (NP) dimensions in related to the decoration technique and the film thickness were investigated. Materials and Methods Black phosphorus microcrystals were suspended in dimethylsulfoxide and kept under ultrasonication for several hours. The exfoliated bP nanosheets were decorated with nickel nanoparticles following two different procedures: 1) preformed Ni NPs were immobilized on bP, 2) Ni NPs were grown directly on bP flakes. Electrical conductance measurements have been performed on Ni/bP flakes deposited via spin coating on Al2O3 substrates with built-in interdigitated gold electrodes, in order to better control the film thickness. Electrical conductance measurements have been performed at RT (25±2°C) by exposing the sensing film to certified mixtures of NO2 diluted in dry air (20% O2 and 80% N2) with different NO2 concentration ranging from 200 ppb to 1 ppm. Results and Conclusions Exfoliated black phosphorus nanoflakes decorated with nickel nanoparticles (Ni/bP) have been prepared and characterized with particular attention to the role of Ni nanoparticle dimension in the sensing mechanism. Electrical activity towards different concentrations of NO2 at room temperature in a dry air environment highlighted fast and stable response over the time. This latter characteristic is particularly relevant since environmental instability of exfoliated BP has been an issue so far, under ambient conditions few-layer bP degrades completely in less than a week, preventing its applications in several fields. In situ grown Ni/bP (2) shows stable response during all the four weeks measurements period with no dependence of the response on the film thickness. Ni decoration effectively suppress ambient degradation, for at least 1 week in Ni/bP (1) and over 4 weeks in Ni/bP (2) in ambient conditions. This result highlighted that Ni/bP (2) sensor can be practically used under ambient conditions for a reasonable period without performance degradation of the devices.The obtained results pave the way for the use of chemically exfoliated bP flakes for gas sensing applications, avoiding the use of a time-consuming technique for the exfoliation and for the fabrication of the metallic contacts, like electron beam lithography, focused ion beam lithography, etc.

Atmospheric nitrogen dioxide at different concentrations levels regulates growth and photosynthesis of tobacco plants

ABSTRACT Nitrogen dioxide (NO2) is recognized as a toxic gaseous pollutant. However, an appropriate concentration of NO2 can promote the growth of plants. In this study, tobacco was exposed to different concentrations of NO2. The results that 1, 4, and 8 μL L−1 NO2 fumigation increased the net photosynthetic rate (P n), maximum photochemical efficiency (F v/F m) and light energy utilization capacity parameters (PI ABS) of leaves, and promoted the growth of seedlings. About 16 μL L−1 NO2 caused the leaves to wither, and the plants were about to die after five days of fumigation. About 8 μL L−1 NO2 obviously promoted the growth of plants, but meanwhile, the old leaves began to show signs of damage, such as bruising and yellowing. Therefore, 8 μL L−1 may be the threshold concentration of herbaceous plants with high NO2 assimilation ability. At an intermediate concentration (4 μL L−1) within the threshold range, NO2 is most beneficial to the growth of herbaceous plants.

Low-cost Fabrication of Cu doped ZnO (Zn0.95Cu0.05O) Film for Enhanced Gas Sensing Applications

Cu doped ZnO film (Zn0.95Cu0.05O) was fabricated by simple and cost-effective screen printing method. The structural and optical properties of prepared film was studied through X-ray diffraction (XRD) and UV-Vis spectroscopy techniques respectively. XRD analysis revealed the polycrystalline nature of prepared film with hexagonal structure. The optical band gap determined from UV-Vis analysis was found to be 3.40 eV. The gas sensing performance of prepared film was studied at room temperature toward different concentrations of NO2 ranging in between 1ppm – 5ppm. The response and recovery time was noted as 13s and 92s respectively. All these outcomes shows that the Cu doped ZnO film shows enhanced gas sensing performance and can be utilized for industrial scale production of gas sensors.

Visible light assisted room-temperature NO2 gas sensor based on hollow SnO2@SnS2 nanostructures

SnS2 is a promising candidate for NO2 sensing applications due to its suitable band gap and large electronegativity. However, SnS2 based gas sensors are still restricted to detect NO2 gas at room temperature due to their giant resistance and poor recovery. Here, we report hollow SnO2@SnS2 nanostructures prepared by a one-step hydrothermal method. The SnO2@SnS2 based sensor showed high response and good recovery to ppb-level NO2 under visible illumination at room temperature (25 °C). The superior sensing performance of the SnO2@SnS2 sensor was attributed to the hollow porous heterojunction structure beneficial for gas diffusion, as well as visible light assistant facilitating charge transfer and gas desorption. This work systematically studied the influence of oxygen concentration in background gas on the NO2 sensing performance of the SnO2@SnS2 sensor, and proposed a physical adsorption model for the NO2 sensing mechanism of the SnO2@SnS2 sensor under visible light at room temperature. In addition, the effect of humidity on the gas sensing performance of the SnO2@SnS2 sensor to different concentrations of NO2 was also discussed.

Preparation of palladium oxide nanoparticles supported on tin oxide nanofibers via modified electrospinning for ultra-low ppb NO2 detection

Herein, we describe the fabrication of a gas sensor based on self ordered SnOx nanofibers decorated with PdOx nanoparticles by using a simple, flexible and scalable approach. The sensing material was synthesized and integrated onto screen printed microceramic platform using modified electrospinning. Material morphology and structure were addressed by Field Emission Scanning Electron Microscopy (FESEM), High Resolution Transmission Electron Microscopy (HRTEM) and X-Ray Diffraction analysis (XRD). Moreover, X-ray Photoelectron Spectroscopy (XPS) confirmed the successful grafting of palladium ions onto the nanofiber outer wall.In an attempt to fully replicate the real working conditions of a gas sensor, the electrical measurements were performed upon exposure of the sensor to different concentrations of NO2 diluted in humid air. PdOx@SnOx sensor demonstrated a remarkable sensitivity towards NO2 with good linearity and detection limit around 10 ppb under humid air. Furthermore, the sensor exhibited an ultra weak cross sensitivity towards interfering air pollutants present at high ppm level such as CO and NH3 at 325 °C. For comparison, the reference sensor based on bare SnOx showed a degraded response towards tested gases under humid ambient. This proves the potential of the hybrid sensor preparation protocol regarding its future application for the detection and quantification of low levels of NO2 in air.

Nickel-Decorated Black Phosphorus for Room Temperature NO2 detection

We study the electrical characterization at room temperature (RT) of black phosphorus nanoflakes decorated with nickel nanoparticles (Ni/bP). The latter has been exposed to different concentrations of NO2 at RT in a dry air environment highlighting fast and stable response over the time. This latter characteristic is particularly relevant since environmental instability of exfoliated BP has been an issue so far, under ambient conditions few-layer BP degrades completely in less than a week, preventing its applications in several fields. Introduction In the rapidly emerging field of layered two-dimensional (2D) functional materials, bP, the all P-counterpart of graphene, is a potential candidate for various applications e.g., nanoscale optoelectronics, rechargeable ion batteries, electrocatalysts, thermoelectrics, solar cells, and sensors [1]. bP has been reported to exhibit superior chemical sensing performance. In particular, bP is selective for the detection of paramagnetic molecules, e.g., NO2, in addition to high sensitivity at a limit of detection (LOD) of ppb levels.[2] In this work, by applying a multiscale characterization approach we demonstrated a stability and functionality improvement of Nickel-decorated bP (Ni/bP) films for gas sensing prepared by a simple, reproducible and affordable deposition technique. Furthermore, we studied possible electrical activity of these films for their employment as functional layers in gas sensors by exposing them to different gaseous compounds (NO2, CO2, H2, NH3, CO, Benzene, etha-nol, ethylene, Formaldehyde) in different relative humidity (RH%) conditions. Moreover, the influence in sensing perfor-mance of nickel nanoparticle (NP) dimensions in related to the decoration technique and the film thickness were investigated. Materials and Methods Black phosphorus microcrystals were suspended in dimethylsulfoxide and kept under ultrasonication for several hours. The exfoliated bP nanosheets were decorated with nickel nanoparticles following two different procedures: 1) preformed Ni NPs were immobilized on bP, 2) Ni NPs were grown directly on bP flakes. Electrical conductance measurements have been performed on Ni/bP flakes deposited via spin coating on Al2O3 substrates with built-in interdigitated gold electrodes, in order to better control the film thickness. Electrical conductance measurements have been performed at RT (25±2°C) by exposing the sensing film to certified mixtures of NO2 diluted in dry air (20% O2 and 80% N2) with different NO2 concentration ranging from 200 ppb to 1 ppm. Results and Conclusions Exfoliated black phosphorus nanoflakes decorated with nickel nanoparticles (Ni/bP) have been prepared and characterized with particular attention to the role of Ni nanoparticle dimension in the sensing mechanism. Electrical activity towards different concentrations of NO2 at room temperature in a dry air environment highlighted fast and stable response over the time. This latter characteristic is particularly relevant since environmental instability of exfoliated BP has been an issue so far, under ambient conditions few-layer bP degrades completely in less than a week, preventing its applications in several fields. In situ grown Ni/bP (2) shows stable response during all the four weeks measurements period with no dependence of the response on the film thickness. Ni decoration effectively suppress ambient degradation, for at least 1 week in Ni/bP (1) and over 4 weeks in Ni/bP (2) in ambient conditions. This result highlighted that Ni/bP (2) sensor can be practically used under ambient conditions for a reasonable period without performance degradation of the devices.The obtained results pave the way for the use of chemically exfoliated bP flakes for gas sensing applications, avoiding the use of a time-consuming technique for the exfoliation and for the fabrication of the metallic contacts, like electron beam lithography, focused ion beam lithography, etc.

Highly fluorescent dihydropyrimido-diindole derivative as a probe for detecting nitrite in food products and cell-imaging

One-pot reaction approach to the synthesis of dihydropyrimido-diindole fluorophores (DPDI) was developed. In DPDI molecules, the two pyrrole rings in dipyrromethane were bridged by a carbon atom, eliciting a six-membered ring and rigid planar structure. Photophysical measurements demonstrated that DPDI can exhibit strong fluorescence, large Stokes shift and low sensitivity to pH. Cyclic voltamogram indicated a pair of redox peaks of DPDI near ±0.48V, implying that DPDI can be oxidized by nitrite (NO2−). In the presence of NO2−, DPDI showed apparent change in colours and fluorescence intensity owing to the implantation of NO2−. From this basis, a highly sensitive and selective analysis of NO2− was established using DPDI as probes, which offered a sensitive determination of NO2− in the concentration range of 0–17 μM with the detection limit of 2.2 nM. Furthermore, DPDI was employed for fluorescence imaging, demonstrating the ability to discriminate from different concentrations of NO2− in living cells. The newly developed DPDI dyes showed the obvious advantages of facile preparation and large Stokes shift over conventional dipyrrole-based phosphors.

Intrinsically ESIPT-exhibiting and enhanced emission in polymer nanoparticles as signaling for sensing nitrite.

A straightforward approach to the fabrication of intrinsically excited-state intramolecular proton transfer (ESIPT)-fluorescent polymer nanoparticles (e-PNPs) was developed. The e-PNPs were obtained by self-assembly of the homopolymers derived from 4-aminosalicylic acid in aqueous solution. By incorporating ESIPT modules into polymer nanoparticles, the ESIPT reaction can be endowed with moderate hydrophobic micro-environment by nanoparticle scaffolds, eliciting enhanced ESIPT emission. The newly developed e-PNPs exhibit strong tautomeric fluorescence(e-FL), good photostability, low-toxicity and favourable biocompatibility in aqueous solution. Upon the addition of NO2-, the e-FL can be significantly quenched owing to the reaction of NO2- with the amide groups on e-PNPs. From this basis, the fluorescence detection of NO2- was implemented, which showed a linear relationship between 0 nM and 110 nM with a detection limit of 2.3 nM. Furthermore, e-PNPs were used as nanoprobes to monitor the NO2- levels in HeLa cells by fluorescence imaging, demonstrating the ability of discrimination from different concentrations of NO2-. The proposed method can be applied to a wide range of other ESIPT modules to integrate into polymer nanoparticles and offer highly sensitive nanosensing platform for bioanalysis and molecular imaging.

CdS coated clad-modified fiber optic sensor for detection of NO2 gas

In this investigation, a clad-modified fiber optic sensor is reported for NO2 gas detection. CdS is coated over cladding-removed region by Chemical Bath Deposition (CBD) which acts as the gas-sensing medium. CdS is coated over four fibers each with a different coating duration of 10, 20, 30 and 40 min. Characterisation of CdS is done by Scanning Electron Microscope (SEM), Energy-dispersive x-ray spectroscopy (EDX), x-ray Diffraction (XRD), Photoluminescence study (PL) and UV-visible absorption spectroscopy. The spectral response for different concentrations of NO2 is studied on the four fibers separately, and it is analysed.